Autonomous stratospheric airship

ABSTRACT

An autonomous stratospheric airship comprising a hull which contains an equipment bay, forward and aft ballonets, forward and aft air management sub-systems, a propulsion system, and a control system is described. The airship also comprises a regenerative solar energy power and storage sub-system which allows powered daytime and nighttime operations. Further, the control system of the airship enables autonomous operation between selected waypoints or along a specified line of sight. The solar arrays utilized by the airship are internally mounted and gimballed so as to provide maximum collection efficiency and not impede the aerodynamic profile of the airship. A greatly simplified and slightly less controllable version of the airship, which makes use of alternative solar array control and ballast management systems, while carrying the equipment bay on the exterior of the hull, is also disclosed.

This application is a divisional application of U.S. patent applicationSer. No. 09/247,878, now pending, filed Feb. 15, 1999.

GOVERNMENT LICENSE RIGHTS

The U.S. Government has a paid-up license in this invention and theright in certain circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Contract No.F41621-93-05006 T.O. 0026 for the Joint Command and Control WarfareCenter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of lighter-than-air typecraft and, more particularly, to an autonomous stratospheric airshiphaving a neutrally buoyant structure at flight altitude, making use ofregenerative electric energy storage and collection. This applicationclaims the benefit of U.S. Provisional Patent Application No.60/111,835, filed on Dec. 11, 1998.

2. Description of the Related Art

In the past, there have been designed and used a series of dirigibles,other types of lighter-than-air vehicles, hot-air balloons, and soforth, for passenger transport, rescue work, lift capabilities, andtransport of goods and supplies. The present invention relates to apowered airship having a buoyant structure designed specifically foroperations in the stratosphere. It incorporates an autonomous navigationcapability and a regenerative solar electric energy collection andstorage system, enabling the airship to remain aloft for extendedperiods of time, while following a specified course and gatheringmission-specific data.

The prior art reveals several attempts at providing a portion of thecapabilities embodied in the present invention, but none was found toincorporate all of the capabilities mentioned below and each suchattempt tends to utilize rather complicated mechanical structures. U.S.Pat. Nos. 5,333,817 and 5,538,203 both disclose a buoyancy adjustmentsystem for a lighter-than-air vehicle, involving a series of ballonets,each arranged along the longitudinal axis of the airship in equalnumbers. The object of these inventions is to provide a system ofindependent control for ballonet inflation/deflation which dispenseswith ducted coupling to the individual ballonets. In addition, U. S.Pat. No. 5,538,203 provides rapid deflation of the same ballonet system,instead of merely venting it to the atmosphere. In either case, thissystem is rather primitive and does not take into account thedifferential pressure between the atmosphere, the surrounding airshipgas bag, and the pressure within individual ballonets.

U.S. Pat. No. 5,348,254, issued to Nakada, claims an airship design forflights of long duration powered by solar cell batteries and a hydrogengeneration system. This system obviates the need for batteries byelectrolytic generation of hydrogen; however, accidental puncture of thehydrogen storage envelope can easily result in complete destruction ofthe airship.

U.S. Pat. No. 4,995,572, issued to Piasecki, describes a multi-stage,high-altitude data acquisition platform comprising the combination of alow-altitude dirigible and a stratospheric balloon for use at 60,000 ft.and above. The primary object of this invention is to provide a stablelaunch platform for lifting heavy payloads to stratospheric altitudes.The airship contains a silo used to retain the stratospheric balloon forlaunch from low altitudes. Such a multi-vehicle payload lifting systemis rather complex and unnecessary for accomplishing the advantages andobjectives of the present invention.

U.S. Pat. No. 4,204,656 issued to Seward III, discloses a bi-axialpropulsing control system for airships. This system, as illustrated inthe patent drawings, does not distribute the propulsion motor loadingequally among the ascent/descent and left/right movement axes. Inaddition, the torquing forces of the propulsion motor are applied at theends of the orientation axes, causing greatly increased loading on thepropulsion direction drive system.

French Patent No. 86 02734 discloses a dual-axis, symmetric propulsionsystem for airships. This system comprises a set of two or more motorswhich move in concert to direct the motion of the airship. Thisapplication requires a plurality of motors, unnecessary toimplementation of the present invention.

U.S. Pat. No. 4,934,631, issued to Birbas, describes a lighter-than-airvehicle comprising a framework surrounded by a series of inflatable liftbags. Each bag contains a heating element and lifting gas. Thepropulsion system comprises a shrouded propeller with vanes to directthe propulsive force. While this airship makes use of a singlepropulsion unit to navigate through the air, it entails a complicatedassembly structure which is impractical for inexpensive construction. Inaddition, the airship has no means of autonomous navigation ormaintaining station above a fixed point of the surface of the earth inautonomous fashion.

Japanese Patent No. 5-221387A discloses an airship constructed oftransparent materials wherein a solar array is disposed to receiveenergy from the sun. However, this design is not constructed formultiple-axis array adjustment to capture the maximum amount of solarenergy based on the airship position in relation to the sun. Only asingle, longitudinal, axis of rotation for the array is shown. Otherpatents, such as Japanese Patent No. 54-35994, U.S. Pat. No. 5,518,205issued to Wurst et al., and U.S. Pat. No. 4,364,532 issued to Stark, alldescribe solar-powered airships with solar cells disposed on the surfacestructure of the ship. Again, the inherent disposition of the cellstructure precludes the use of optimal positioning of the cells tocapture the maximum amount of solar energy to be gained given a variedposition of the airship in relation to the sun.

None of the aforementioned inventions are directed toward an autonomousplatform specifically designed for flight in the lower stratosphere. Inaddition, none are directed toward an airship which is capable ofcontrolling operational altitude, including maintenance of a fixedposition over a point on the surface of the earth, or navigation betweenpredetermined waypoints. Further, none of the prior art is directedtoward an autonomous airship having a specially constructed solar arrayenergy extraction source which provides sufficient energy for powerduring the day, and stores sufficient energy for continuous night-timeoperation.

Therefore, it is desirable to have an autonomous airship specificallydesigned for flight in the lower stratosphere, with the ability tomaintain a fixed position over a point on the surface of the earth, ornavigate between predetermined waypoints. Additionally, it is desirableto have an autonomous airship capable of controlling its operationalaltitude, using ballonets to control the pitch axis attitude.Furthermore, it is desirable to have an autonomous airship which uses asingle motor for propulsion that evenly distributes the propulsiveforces along the directive axes of the articulating means. It is alsodesirable to have an autonomous airship which can utilize solar energyto power propulsion during the day and additionally, store sufficientenergy for continuous operation throughout the night.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an autonomousairship designed specifically for flight in the lower stratosphere withthe capability for maintaining a fixed position over a point on thesurface of the earth is disclosed. Additionally, the airship providesautonomous control and navigation between predetermined waypoints, ormay be programmed to remain within the optical line of sight of apredetermined position on the surface of the earth by matching the speedof the wind.

Other features of the airship embodying the present invention includeconstruction from high strength, light-weight, polymer-based filmmaterials for strength, and transparent/translucent material forcollection of solar energy by internally-mounted solar arrays. Theautonomous airship can be launched in an uninflated condition and doesnot require control or propulsion during ascent. The internally mountedarrays reduce aerodynamic drag, provide a pointing capability formaximum solar energy collection, are cooled by an air duct, and arecontained within a separate chamber which permits access to the arraysfrom the outside of the airship.

The airship embodying the present invention may include a hull definingan enclosed cavity, a lifting gas, a forward ballonet, an aft ballonet,and an equipment bay disposed within the cavity, the bay defining anenclosed chamber, and an overall air management subsystem, at least onesolar array, a multiplicity of energy storage units, and an autonomouscontrol system disposed within the bay, the chamber being in fluidcommunication with the forward and aft ballonets; a propulsion systemattached to the hull and in electrical communication with at least onesolar array and the energy storage units; and a multiplicity of tailfins attached to the hull. The air management subsystem may furthercomprise a forward air management subsystem having a blower and an aftair management subsystem, the forward air management subsystem being influid communication with the forward ballonet and the bay, and the aftair management subsystem being in fluid communication with the aftballonet and the bay. The forward air management subsystem may comprisea forward ballonet pressure sensor and the aft air management subsystemmay comprise an aft ballonet pressure sensor. The forward and aft airmanagement subsystems may also each comprise a lifting gas releasevalve, the valves being in fluid communication with the hull.

The propulsion system of the present invention may further comprise agimbal housing, a motor and transmission assembly, a motor pivot, and apropeller, the housing being fixedly attached to the hull and pivotallymounted to the pivot, the pivot being fixedly attached to the motor andtransmission assembly, the assembly being attached to the propeller.

At least one solar array may be aligned with the central axis of thehull, and may be gimballed about respective elevation and azimuth axesof the array. At least one solar array may provide electrical power tothe propulsion system during daytime flight operations and themultiplicity of energy storage units may provide electrical power to thepropulsion system during night time flight operations.

The autonomous control system of the present invention, the overall airmanagement subsystem, and the propulsion system may provide navigationalcontrol between selected waypoints, wherein the autonomous controlsystem may include a GPS receiver and a compass. Therefore, the overallair management subsystem, the autonomous control system, and thepropulsion system may be adapted to control movement of the airshipabout its center of gravity.

The hull of the present invention may have an outer surface and amultiplicity of tail fins may be disposed in a first position contiguouswith the outer surface of the hull during ascent to flight altitude andthe multiplicity of tail fins may move to a second positionnon-contiguous with the surface of the hull as the hull inflates due toa reduction in atmospheric pressure.

The present invention may also include, as an alternative embodiment, ahull defining an enclosed cavity; a lifting gas and at least one solararray disposed within the cavity; a forward ballast reservoir; an aftballast reservoir; a ballast management subsystem attached to the hulland in fluid communication with the forward and aft ballast reservoirs;an equipment bay attached to the hull, the bay having a multiplicity ofenergy storage units and an autonomous control system; a propulsionsystem attached to the hull and in electrical communication with atleast one solar array and the energy storage units; and a multiplicityof tail fins attached to the hull. The ballast management subsystem mayfurther comprise fluid lines between the forward and aft ballastreservoirs, a ballast valve, and a ballast exhaust.

The alternative embodiment airship propulsion system of the presentinvention may further comprise a gimbal housing, a motor andtransmission assembly, a motor pivot, and a propeller, the housing beingfixedly attached to the hull and pivotally mounted to a pivot, the pivotbeing fixedly attached to a motor and transmission assembly, theassembly being attached to the propeller.

In this alternative embodiment at least one solar array may be alignedwith a central axis of the hull, and the array may be gimballed aboutrespective elevation and azimuth axes of the array. At least one solararray may provide electrical power to the propulsion system duringdaytime flight operations and the multiplicity of energy storage unitsmay provide electrical power to the propulsion system during night timeflight operations.

The autonomous control system, the ballast management subsystem, and thepropulsion system in this alternative embodiment of the presentinvention may provide navigational control between selected waypoints,wherein the autonomous control system may include a GPS receiver and acompass. Therefore, the ballast management subsystem, the autonomouscontrol system, and the propulsion system may be adapted to controlmovement of the airship about its pitch and yaw axes.

The hull in the alternative embodiment of the present invention may havean outer surface and a multiplicity of tail fins may be disposedcontiguous with the outer surface of the hull during ascent to flightaltitude, wherein the multiplicity of tail fins may move to a secondposition non-contiguous with the surface of the hull as the hullinflates due to a reduction in atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a first embodiment of the autonomous airship ofthe present invention.

FIG. 2 is a schematic block diagram of the pressurization system for theballonets within the first embodiment.

FIG. 3 is a side view of a forward ballonet air management subsystem.

FIG. 4 is a side view of an aft ballonet air management subsystem.

FIG. 5 is a perspective view of the propulsion system for an airship.

FIG. 6 is a side view of the equipment bay assembly for the firstembodiment.

FIGS. 7A and 7B are perspective views of one of the internally-mountedsolar array panels which provide electric power to the first embodiment.

FIG. 8 is a schematic block diagram of the power supply system for thefirst embodiment.

FIG. 9 is a block diagram of the controller interface circuitry fordirecting autonomous airship operations.

FIG. 10 is a perspective view of an airship illustrating variousmovement axes.

FIG. 11 is a side view of a second, alternative embodiment of theautonomous airship of the present invention.

FIG. 12 is a schematic view of the ballast management subsystem for asecond, alternative embodiment of the autonomous airship of the presentinvention.

FIG. 13 is a perspective view of the rectangular solar array assemblyfor a second, alternative embodiment of the autonomous airship of thepresent invention.

FIG. 14 is a schematic block diagram of the power supply subsystem for asecond, alternative embodiment of autonomous airship of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 1, a side view of the first embodiment of theautonomous stratospheric airship 10 can be seen. The hull 20 is madefrom a clear or relatively transparent polymer-based film, preferably0.5 mm thick. The material is selected to withstand pressures resultingfrom changes in lifting gas temperatures contained within. The hull 20is shaped as a stream-lined body with a hemispherical front and aconical rear, and the overall size is determined by the mass of thepayload 390, while the length to width ratio is preferably 5:1. As theresult of experimentation, it has been found that a design capable ofcarrying 18 pounds of useful load to 70,000 feet is approximately 125feet long, and 25 feet in diameter.

Attached to the conical section of the hull 20 are a multiplicity ofself-deployed tail fins 90, preferably three in number. The fins 90 arepreferably made of the same film material as the hull 20. The fins 90are supported by a self-erecting mechanism that deploys as the hull 20body inflates during ascent. The hull 20 center of buoyancy iscontrolled by two internal ballonets, forward ballonet 40 and aftballonet 50. Each ballonet can be used independently to control thelocation of the center of buoyancy, consequently effecting the airship's10 movement about the pitch axis 745 (see FIG. 10). Alternatively, theballonets 40 and 50 can be used together to cause the airship 10 toascend or descend.

The airship 10 completely encloses an internal equipment bay 30 chamberwhich houses solar arrays 340, forward and aft air managementsub-systems 60 and 70, a control system 390, and a mission-specificpayload. While the hull 20 is filled with lifting gas comprisinghydrogen, helium, or ammonia, the bay 30 is filled with air drawn fromthe atmosphere outside of hull 20 and is circulated within the bay 30for cooling of internal components. The bay 30 can also be pressurizedand so function as an additional buoyancy control mechanism for airship10. To maintain the integrity of hull 20, the contents of bay 30 can beaccessed from the exterior of airship 10 by means of a zipper, zip-lockplastic closure or other relatively air-tight closure (not shown).

FIG. 2 depicts a schematic block diagram of the pressurization systemused to control the air flow and pressurization of the equipment bay 30and the forward and aft ballonets 40 and 50. Forward ballonet 40 isconnected to forward ballonet valve 160 by way of forward ballonetfill-tube 162. Forward ballonet pressure sensor 110 is used to monitorthe pressure differential between the forward ballonet 40 and thelifting gas pressure within hull 20. Forward ballonet valve 160 is alsoconnected to the atmosphere within the equipment bay 30 by way offorward ballonet equipment bay intake 164. Forward ballonet 40 mayexhaust air to the atmosphere external to the hull 20 by means offorward ballonet atmospheric exhaust 166. Thus, forward ballonet 40 maytake in air from the atmosphere surrounding hull 20 by way of forwardballonet equipment bay intake 164, or exhaust air to the atmospheresurrounding hull 20 by way of forward ballonet atmospheric exhaust 166.

Similarly, rear ballonet 50 is connected to aft ballonet valve 210 byway of aft ballonet fill tube 212. The differential pressure between theaft ballonet 50 and the lifting gas within hull 20 is measured by aftballonet pressure sensor 150. Aft ballonet 50 operates in a mannersimilar to forward ballonet 40; that is, aft ballonet 50 may take in airfrom the atmosphere surrounding hull 20 by way of aft ballonet equipmentbay intake 214, and may exhaust air to the atmosphere surrounding hull120 by way of aft ballonet atmospheric exhaust 216.

The physical implementation of the airship 10 air management sub-systemis illustrated in FIGS. 3 and 4. FIG. 3 depicts a side view of theforward air management sub-system 60, and FIG. 4 depicts a side view ofthe aft air management sub-system 70. Turning now to FIG. 3, it can beseen that the forward air management sub-system 60 provides a housingfor the forward ballonet valve 160, forward ballonet pressure sensor110, equipment bay pressure sensor 120, hull pressure sensor 130, andblower motor 230. Forward air management sub-system 60 also incorporatesa scoop 220 to further assist in air flow control.

During normal operations, the blower motor 230 will take in air from theatmosphere surrounding hull 20 via scoop 220 and pressurize theequipment bay 30 by means of equipment bay atmospheric intake 235 andcheck valve 240, which prevents release of pressurized air fromequipment bay 30 back into the atmosphere. The pressure within the hull20 is monitored by hull pressure sensor 130. In order to pressurize theforward ballonet 40 so as to pitch the airship 10 downward or cause theairship 10 to descend (assuming a similar action by aft air managementsub-system 70), the forward ballonet valve 160 is operated so as todirect pressurized air from the equipment bay 30, through forwardballonet equipment bay intake 164 to the forward ballonet 40 by way offorward ballonet fill tube 162. If it is desired to pitch the airship 10upward or to ascend (assuming a similar action conducted with aft airmanagement sub-system 70), the forward ballonet valve 160 can beoperated so as to exhaust the forward ballonet 40 air by way of theforward ballonet fill tube 162 and the forward ballonet atmosphericexhaust 166 port into the atmosphere surrounding the hull 20 by way ofscoop 220. The operation of scoop 220 is controlled by scoop actuator250. If the pressure within the equipment bay 30 and forward ballonet 40are as desired for a given flight attitude and altitude, then theforward ballonet valve 160 can be operated so as to close off theforward ballonet fill tube 162 and prevent the escape of any air fromthe forward ballonet 40. As a safety measure, hull pressure sensor 130is used to monitor the lifting gas pressure exerted within hull 20 andcan be used to activate a lifting gas relief valve 260 by way of alifting gas release actuator 270 so as to dump lifting gas to theatmosphere and relieve any over-pressure situation within the hull 20.

Turning now to FIG. 4, it can be seem that aft air management sub-system70 is identical to forward air management sub-system 60, with theexception of the sensors housed therein, the blower motor 230, and itsassociated check valve 240. Atmospheric pressure sensor 140 is housed inthe aft air management sub-system 70 enclosure, along with the aftballonet pressure sensor 150. Inflation and deflation of the aftballonet 50 occurs in a similar fashion to that of forward ballonet 40,except that air for the aft ballonet 50 is taken directly from theequipment bay 30, and is supplied from the blower motor 230 located inthe forward air management sub-system 60. That is, the aft ballonet 50is inflated by operation of the aft ballonet valve 210 so as to create apath between the aft ballonet equipment bay intake 214 and the aftballonet fill tube 212. The aft ballonet 50 is deflated by operating theaft ballonet valve 210 so as to create a path between the aft ballonetfill tube 212 and the aft ballonet atmospheric exhaust 216. The scoop220 on the aft air management sub-system 70 can likewise be operated toassist in exhausting air from the aft ballonet 50.

The aft air management sub-system 70 also has the capability ofdepressurizing the hull 20 by activating a lifting gas relief valve 260by means of lifting gas release valve actuator 270. By operating the aftballonet valve 210 so as to create a path between the equipment bayintake 214 and the equipment bay outlet valve 200, it is also possibleto exhaust air from the equipment bay 30 into the atmosphere surroundingthe hull 20.

The airship 10 is propelled by a propulsion system 80 comprising apropeller 300, driven by a motor and transmission assembly 330, as shownin FIG. 5. Left and right directional control of the airship 10 isprovided by moving the motor and transmission assembly 330 about theaxis of the motor pivot 320, which is mounted within the gimbal housing310. The propeller 300 is preferably a three-bladed fixed-pitch type,but a variable-pitch type propeller 300 may be used without detractingfrom the spirit of the invention. Those skilled in the art will readilyrecognize the advantages and disadvantages involved in choosing betweenthese two types of propellers.

FIG. 5 also illustrates the tail fins 90 of the airship 10, which areused to enhance in-flight stability about the pitch axis 745, yaw axis725, and the hull central axis (or roll axis) 420 of the airship 10 (seeFIG. 10). Tail fins 90 are most preferably three in number, and eachcomprise a pivoting mast 305 connected to a fin pivot 307. This mannerof construction allows each of the tail fins 90 to lay along the surfaceof the hull 20 of the airship 10 during initial launch and, as the hull20 begins to expand due to the decrease in atmospheric pressuresurrounding it, the tail fins 90 will deploy into their extendedposition away from hull 20 (as illustrated in FIG. 5) due to therotation of the mast 305.

FIG. 6 illustrates the equipment bay 30 and its contents comprisinginternallygimballed solar arrays 340, energy storage units 350,emergency system 360, autonomous control system 390, communicationssystem 380, and the emission-specific payload 370. As mentionedpreviously, the forward and aft air management sub-systems 60 and 70 canbe used to pressurize and exhaust the equipment bay 30. In addition, theconstant induction of air by way of forward air management sub-system 60into equipment bay 30 can be used to cool the contents of equipment bay30, especially solar arrays 340. Pressurizing the equipment bay 30 withair from the atmosphere surrounding hull 20 also serves as an additionalbuoyance control mechanism for the airship 10.

All of the energy used to power the propulsion system 80 is provided bythe solar arrays 340. During the day, solar energy can be directlyapplied to the propulsion system 80, while night time energy is suppliedby energy storage units 350, preferably deep-cycle batteries well knownin the art, which are charged by the solar arrays 340 during the day.

The solar energy collection system consists of a multiplicity of arrays340 that are installed within the equipment bay 30, which is locatedwithin the hull 20. As shown in FIGS. 7a and 7 b, the arrays 340 aremounted on gimbals, denoted as azimuth rotation pivot 400 and elevationrotation pivot 410. These two axes of rotation, combined with theorientation of the arrays 340 along the hull central axis 420, allowpointing the solar array 340 panels to obtain maximum collectionefficiency, regardless of the position of the airship 10 with respect tothe sun. Internally mounting arrays 340 permit operation of the airship10 without the associated aerodynamic drag of externally mounted solarpanels. In addition, the construction of the airship 10 makes itpossible to duct cooling air around the arrays 340 and other contents ofthe equipment bay 30 without breaching the integrity of the main hull20, which also serves as the main lifting gas chamber. The equipment bay30 is equipped with any of several closures well known in the art, suchas zippers or plastic zip-lock devices (not shown) which provide directaccess through the equipment bay 30 for installation servicing of theequipment at any time prior to launch, without affecting the integrityof the hull 20. The transparency or translucency of the hull 20 can bevaried to affect the amount of solar energy collected by the arrays 340.

Turning now to FIG. 8, the components for the energy provision andstorage system for the airship 10 can be seen. Each solar array 340 ismoved about its azimuth rotation pivot 400 by means of an azimuth motor450, which is directed by an azimuth controller 440, and powered by anazimuth power source 430, derived from energy storage units 350distributed throughout the equipment bay 30. Similarly, the arrays 340are moved about their elevation rotation pivots 410 by an elevationmotor 510, which is directed by an elevation controller 500 and poweredby an elevation power source 490, also derived from energy storage units350.

The activity of azimuth controller 440 is effected by the azimuthmeasurements derived from the azimuth feedback signal 480, provided bythe azimuth transducer 460. Similarly, the activity of elevationcontroller 500 is influenced by the elevation feedback signal 540provided by the elevation transducer 520. Both the azimuth and elevationcontrollers 440 and 500 are programmed to operate by way ofproportional, integral, or derivative control, or some combination ofthese methods, as is well known in the art. Other feedback-based controlsystems are also anticipated by the present invention.

During the day, solar arrays 340 are connected so as to provide arelatively high motor drive voltage to the day drive service bus 630,preferably about 136 volts DC. The solar array current 610 and solararray voltage 620 are monitored by the autonomous control system 390(not shown). Step down converter 645 operates to supply a batterycharger/monitor 650 with sufficient current to charge the energy storageunits 350 during daytime operations. Energy storage units 350, which mayconsist of lithium-ion batteries, or other sources of storage well knownin the art, are monitored with respect to several parameters, includingbattery voltage 670, battery current 690, and battery temperature 700.If necessary, battery heaters 660 can be activated to bring the energystorage units up to a predetermined charging or operational temperaturefor a maximum efficiency. The monitored parameters are communicated tothe autonomous control system 390 and communications system 380 by wayof a control communication interface 680.

During nighttime operations, the propulsion system 80 is powered by wayof night drive service bus 640. The night drive voltage 550, night drivecurrent 560 and converter temperature 570 are also monitored. Theresulting data is also communicated to the autonomous control system 390and communication system 380.

The voltage derived from the step-down converter 645 and used toenergize the night drive service bus 640 and the battery charger/monitor650, can be further reduced by way of step-down converters 720, and usedto power various payload 370 requirements. A standard avionics powerbus, namely, ship service bus 710, provides a standardized DC voltage tothe contents of the equipment bay 30. The ship service bus 710 ispreferably operated at a voltage of 28 volts DC.

An array temperature transducer 600, powered by a transducer powermodule 590 is used to determined the temperature of the solar arrays byway of an array temperature transducer 580. If the arrays 340 exceedsome pre-determined temperature, then the forward and aft air managementsub-systems 60 and 70 can be activated to cool the arrays 340 to adesired temperature. The array temperature monitoring activity, as wellas the cooling activity are directed by the autonomous control system390.

FIG. 9 illustrates a block diagram of the autonomous control system 390.While preferably implemented with a central processor 800 whichcommunicates via a multiplicity of serial channels 810 and ananalog-to-digital converter 815. However, specialized and more complexinterfaces, such as may be utilized by the airship 10 energy storagesystem, the front and rear air management sub-systems 60 and 70, and thepropulsion system 80, may be specially constructed and implemented as asolar cell and battery interface 860, a front air management sub-systeminterface 870, a rear air management sub-system interface 880, and apropulsion interface 890. Payload interface 900 will normally bespecially constructed to interface to whatever mission-specific payload370 is carried by the airship 10. A Global Positioning System satellite(GPS) receiver 820, electronic compass 830, command/control receiver840, and telemetry transmitter 850 are also employed by the airship 10to complete the autonomous control function. Included within thecapabilities of airship 10 is the transmission of acquired data from thevarious transducers and sensors on board airship 10, and the payload370. Command/control receiver 840 enables the reception of operationaland emergency instructions from the ground control station (not shown)which monitors the progress of the airship 10 on any specific mission.The GPS receiver 820 enables exact positional monitoring and control ofthe airship 10, while the electronic compass 830 provides fordead-reckoning capability during periods where the GPS receiver 820 isincapable of proper function. The autonomous control system 390,combined with the operation of the air management sub-systems 60 and 70,and the propulsion system 80, provide an airship 10 capable ofautonomous operation between pre-selected or commanded waypoints. Theinternally-gimballed solar arrays 340 can be pointed for maximumcollection efficiency based on geographical location, date, and time.Command control and data reception can also be interactively applied tothe payload 390.

The autonomous control system can be programmed to select differentspeeds for day and night operations to maintain the average location ofthe airship 10 over a specified point on the surface of the earth.Properly selected, the speed schedule selected for airship 10 willoptimize use of the solar arrays 340 and the energy storage units 350 tomaximize the average speed of the airship 10. When the prevailing windsare less than the maximum airship 10 design speed, excess power isavailable to reposition the airship 10 with respect to the pitch axis745, yaw axis 725, and the hull central axis 420, as illustrated in FIG.10.

The propulsion system 80 propels the airship 10 with forward movement770 as long as the electric power available to the motor andtransmission assembly 330 is great enough to overcome the prevailingwinds, less power (or no power) can also be applied to the motor andtransmission 330 so that airship 10 in fact travels with aft movement780. By moving the motor and transmission assembly 330 about the axis ofmotor pivot 320, the line of propulsion for the propeller 300 can bemoved so as to effect left movement 750 or right movement 760 of theairship 10. As mentioned previously, the forward and aft ballonets 40and 50 can also be pressurized independently so as to cause downwardmovement 740 (if both are pressurized), or upward movement 730 (if bothare deflated). The sophisticated combination of autonomous controlsystem 390, combined with the actions of the forward and aft airmanagement sub-system 60 and 70, and the motor pivot 320 of thepropulsion system 80, provide an airship 10 which is completelycontrollable about the airship's center of gravity 790.

The autonomous stratospheric airship 10 can be used for many differentapplications, including provision of a vehicle platform for: largeterrestrial viewing areas with a long flight duration (e.g.exoatmospheric research); communication relay operations (e.g. radiofrequency transponder for voice, data, video etc.; store and forward RFdata; signal interception; or direct broadcast); a terrestrialsurveillance platform with camera and sensors; surveillance of theatmosphere or space; and a platform for scientific and atmosphericresearch.

The autonomous stratospheric airship 10 is designed to be a neutrallybuoyant structure designed specifically for operations in the lowerstratosphere (i.e. 60,000-100,000 feet) it does not require aerodynamiclift, and the hull 20 can be filled with any gas that is lighter thanair, including hydrogen, helium, or ammonia. Use of a thin polymerichull material allows inexpensive and light-weight construction of a hull20 which is able to contain the lifting gas pressure while isolating theequipment bay 30 from the surrounding atmosphere. The airship 10 can belaunched and climbs to altitude much in the same way as a scientificsuperpressure balloon, and no control or propulsion is required toeffect such a launch. The solar regenerative electric energy collectionand storage system provides propulsion during the day and night, andcontinuous operation of powered payloads 370. Internally-gimballed solararrays 340 can be positioned for optimal collection efficiency whilehaving no effect on the aerodynamic profile of the airship 10.

As a way of significantly reducing the cost of providing an autonomousstratospheric airship 10, an alternative embodiment, as shown in FIG.11, is provided by the instant invention. While the size and materialsfor construction of the hull 20 are identical to the embodiment picturedin FIG. 1, in this case, the equipment bay 30′ is located on theexterior of the hull 20, and suspended from the interior of the hull 20by payload suspension lines 905. While a single rectangular arrayassembly 910 is maintained within the hull 20 for providing operativeenergy to the airship 10 during the day, the forward and aft ballonets40 and 50, along with the forward and aft air management subsystems 70are no longer used. However, the propulsion system 80, along with theself-erecting tail fins 90, are retained.

Turning now to FIG. 12, the fluid ballast system 930 can be seen. Thissimplified ballast system, while not providing the capability of theprevious embodiment with respect to altitude control, still enablesadjusting the attitude about the pitch axis 745, as well as in theupward movement 730 direction.

The fluid ballast system 930 comprises a forward ballast reservoir 931,filled with forward fluid ballast 932, connected by way of fluid lines936 to aft ballast reservoir 933, filled with aft fluid ballast 934.Forward and aft fluid ballasts 932 and 934 are moved back and forth byway of by-directional pumps 940 and fluid lines 936, whenever ballastvalve 938 is open so as to provide fluid communication between forwardballast reservoir 931 and aft ballast reservoir 933. To move airship 10in the upward movement 730 direction, the ballast valve of 938 can beopened so as to provide fluid communication between forward ballastreservoir 931 and ballast exhaust 942, or aft ballast reservoir 933 andballast exhaust 942. While a limited amount of directional control ispossible in a downward movement 740 direction, it can only be achievedat the expense of draining helium from the hull 20 by way of a heliumrelease valve 928. Extra helium may be carried in a canister in theequipment bay 30, but such operation is not usually practical, due topayload weight limitations.

FIG. 13 details the rectangular array assembly 910, which comprises arectangular solar array suspended between a Z-axis swivel 913 and aZ-axis drive arm 915 by means of array suspension lines 914. Therectangular solar array 912 is held at two corners between the Y-axisdrive 925 and the Y-axis bearing 926, so as to pivot about the elevationrotation axis 922. Similarly, the rectangular solar array 912 can bemade to pivot about the azimuth rotation axis 924 by driving the Z-axisdrive arm 915 with the Z-axis drive 916. Vertical movement of therectangular solar array 912, due to flexing of the hull 20, isaccommodated by the link arm 918, which allows the Z-axis drive 916 andthe feed-through and mount 920 to move freely. By providing for movementin both the elevation rotation axis 920 and the azimuth rotation axis924, the rectangular solar array 912 can be positioned in whateverlocation is most effective for receiving the maximum amount of solarenergy for conversion into electricity. The suspension system shownallows construction of the rectangular array assembly 910 to be lighterand less expensive than that used for the solar arrays 340 illustratedin FIGS. 7A and 7B. In fact, the rectangular solar array 912 can even beapplied to an inflatable structure, which becomes rigid at flightaltitude, and is flexible on the ground.

FIG. 14 illustrates the power distribution subsystem 950 contained inthe external equipment bay 30∝ utilized by the alternative embodiment ofthe airship 10. In this case, the rectangular solar array 912 providespower to the motor controller 954 by way of a high voltage bus 956. Analternative source of power on this bus 956 are battery packs 964. Therectangular solar array 912 also provides power to an 18 VDC converter958, which in turn energizes a charger 962 for the battery packs 964,and provides power to the system electronics 970 by way of a low-voltagebus 960. The system electronics 970 in this case can be similar to oridentical to the arrangement disclosed in FIG. 9, less the front andrear air management subsystem interfaces 870 and 880. Instead, a singleinterface to the fluid ballast system 930 must be implemented to controlthe bi-directional pumps 940 and the ballast valve 938.

Although the invention has been described with reference to specificembodiments, this description is not meant to be constructed in alimited sense. Various modifications of the disclosed embodiments, aswell as alternative embodiments of the invention will become apparent topersons skilled in the art upon reference to the disclosure herein. Itis, therefore, contemplated that the appended claims will cover suchmodifications that fall within the scope of the invention.

We claim:
 1. An autonomous stratospheric airship comprising: a hulldefining an enclosed cavity, a lifting gas, a forward ballonet, an aftballonet, and an equipment bay disposed within said cavity, said baydefining an enclosed chamber, and an overall air management subsystem,at least one solar array, a multiplicity of energy storage units, and anautonomous control system disposed within said bay, said chamber beingin fluid communication with said forward and aft ballonets; a propulsionsystem attached to said hull and in electrical communication with saidat least one solar array and said energy storage units; and amultiplicity of tail fins, said fins attached to said hull.
 2. Theairship of claim 1 wherein said overall air management subsystem furthercomprises a forward air management subsystem having a blower and an aftair management subsystem, said forward air management subsystem being influid communication with said forward ballonet and said bay, and saidaft air management subsystem being in fluid communication with said aftballonet and said bay.
 3. The airship of claim 2 wherein said forwardair management subsystem further comprises a forward ballonet pressuresensor and said aft air management subsystem further comprises an aftballonet pressure sensor.
 4. The airship of claim 2 wherein said forwardand aft air management subsystems each comprises a lifting gas releasevalve, said valves being in fluid communication with said hull.
 5. Theairship of claim 1 wherein said propulsion system further comprises agimbal housing, a motor and transmission assembly, a motor pivot, and apropeller, said housing being fixedly attached to said hull andpivotally mounted to said pivot, said pivot being fixedly attached tosaid motor and transmission assembly, said assembly being attached tosaid propeller.
 6. The airship of claim 1 wherein said at least onesolar array is aligned with the central axis of said hull, and isgimballed about respective elevation and azimuth axes of said array. 7.The airship of claim 1 wherein said at least one solar array provideselectrical power to said propulsion system during daytime flightoperations and said multiplicity of energy storage units provideelectrical power to said propulsion system during night time flightoperations.
 8. The airship of claim 1 wherein said autonomous controlsystem, said overall air management subsystem, and said propulsionsystem provide navigational control between selected waypoints.
 9. Theairship of claim 1 wherein said autonomous control system includes a GPSreceiver.
 10. The airship of claim 1 wherein said autonomous controlsystem includes a compass.
 11. The airship of claim 1 wherein saidoverall air management subsystem, said autonomous control system, andsaid propulsion system are adapted to control movement of the airshipabout its center of gravity.
 12. The airship of claim 1 wherein saidhull has an outer surface and said multiplicity of tail fins aredisposed in a first position contiguous with said outer surface of saidhull during ascent to flight altitude and wherein said multiplicity oftail fins move to a second position non-contiguous with said surface ofsaid hull as said hull inflates due to a reduction in atmosphericpressure.